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#215890 - 08/11/15 08:18 PM Mysterious Shock  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Well, more of a 'tingle' than a 'shock.' I'm stumped and looking for an explanation ....

First, understand that everything is NEW. From the service to the appliance, all new. Even the power transformer is new.

Today, in seeking to relocate the disconnect serving a ground-source heat pump, I got a mild shock. Almost a gentle tingle. I even felt this from the neutral, as well as the hot lines (on the line side).

Meter readings were in the area of 45-50 vac. Quite a feat for something fed from a new Square-D I-line 3-phase breaker. While I've seen meter 'ghosts,' I've never felt one before. 480v, 60a, undersize neutral for the controls.

Even if the breaker were somehow 'leaking,' what would put the voltage on the neutral? Mind you, this happened with the wires disconnected from the unit, and I was not in contact with the unit at the time.


Work Gear for Electricians and the Trades

#215891 - 08/11/15 09:01 PM Re: Mysterious Shock [Re: renosteinke]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,874
Brick, NJ USA
How is the neutral/ground (earth) terminations within the I-Line?





John

#215892 - 08/11/15 11:15 PM Re: Mysterious Shock [Re: renosteinke]  
JoeTestingEngr  Offline
Member
Joined: Nov 2005
Posts: 791
Chicago, Il.
Reno,
Your situation sounds interesting but I don't quite understand the details. Is there any chance of seeing a sketch?
Joe


#215893 - 08/11/15 11:45 PM Re: Mysterious Shock [Re: renosteinke]  
twh  Offline
Member
Joined: Mar 2004
Posts: 922
Regina, Sask.
If it's on all conductors, maybe they are running a long distance beside other high current conductors.

You can have a difference in voltage between ground points that are a large distance apart.

A floating neutral can produce some odd effects.

Maybe, something nearby is conducting to ground and the source is from the environment. If you can shut breakers off, try turning off the other loads to see if the voltage goes away.


#215894 - 08/12/15 01:02 AM Re: Mysterious Shock [Re: renosteinke]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,135
Estero,Fl,usa
Are you saying you have a few volts on the neutral, in reference to the ground? Not unusual. It is just reflecting voltage drop in the neutral. The only place where neutral = ground is at the main bonding jumper.
Of course if you have a bad connection in there that voltage drop can get pretty big.


Greg Fretwell

#215896 - 08/12/15 10:53 AM Re: Mysterious Shock [Re: renosteinke]  
LarryC  Offline
Member
Joined: Jul 2004
Posts: 783
Winchester, NH, US

Today, in seeking to relocate the disconnect serving a ground-source heat pump, I got a mild shock. Almost a gentle tingle. I even felt this from the neutral, as well as the hot lines (on the line side).

I suspect the ground source heat pump is providing a different ground than the utility ground.

Remember lightning strikes taking out well pumps due to the casing being a better ground electrode.

I suspect the heat pump heat collectors are better grounds than the service earth electrode.


#215898 - 08/12/15 02:02 PM Re: Mysterious Shock [Re: renosteinke]  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
Sounds like Capacitive Coupling - or the Control Circuit's Grounded Neutral Conductor has become re-grounded at or near the Heat Pump.

Simple test to verify the issue is due to Capacitive (or Inductive) Coupling:

  1. Check Voltage between the Ungrounded Conductor and the Equipment Grounding Conductor ("EGC") with a High Impedance Voltmeter (typical DVM),
  2. Shunt one of the Conductors to Equipment Ground via a low Impedance (i.e.: Incandescent Lamp, Solenoid Voltage Tester, full roll of #12, etc.)
    BTW "Shunt To Equipment Ground" = connect the Low Impedance item between one of the Ungrounded Conductors and the EGC
  3. Check Voltage again between the same Ungrounded Conductor and the Equipment Grounding Conductor, with the same High Impedance Voltmeter,
  4. If the issue is Cap / Inductive Coupling, the 40 - 50 VAC will be reduced to, or near zero Volts.


If the issue is not due to a Coupling Effect, and not due to a re-grounded Neutral, call an exorcist!!! wink

--Scott (EE)


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#215899 - 08/12/15 07:00 PM Re: Mysterious Shock [Re: renosteinke]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Exorcist? You never know ...

Joe, this is a typical installation ... PoCo service to a new building. Building receives 480/277V 3-phase and has its' own transformers for 208/120v circuits. Power is fed through a main panel, to separate panels that serve the branch circuits. From there, wires go directly to the heat pump. Yes, there are splices along the way, and other 480/277 circuits in the pipe. The other circuits use #10 wire, as compared to the #6 for the heat pump- so it's not likely the wires got mixed up. All circuits have their own 'dedicated' neutral.

The disconnect is your typical 3-phase disconnect. The disconnect was mounted on a pedestal, and had to be moved over a couple inches to allow for filter changing. Both line and load wires were disconnected from the disconnect.

With the breaker OFF, I still read 45-50v on the 'hot' wires. Later, in the course of my work, I managed to get a slight 'tingle' from one of the hots, as well as the undersized neutral.

Now, twh, you have me questioning the transformer hook-ups. Could there be a floating neutral? Well, it won't hurt to check. The transformers are some sort of "extra efficient" type, so it's possible that there's some detail missed in the installation.


#215900 - 08/12/15 11:16 PM Re: Mysterious Shock [Re: renosteinke]  
JoeTestingEngr  Offline
Member
Joined: Nov 2005
Posts: 791
Chicago, Il.
Well, I would expect that your tingle was from coupling with one or more of the energized wires in the pipe. Were you measuring less between the conductors than you were between each conductor to ground? I would expect that to be the case. Is it practical to LOTO the other ckts that go through the same pipe and about how long a run is it?
Joe
On second thought, I would think that the Neutral to Earth might show the highest reading, since it's connected on one end. It would be almost like you're touching the output of an auto transformer.

Last edited by JoeTestingEngr; 08/12/15 11:22 PM. Reason: addition

#215901 - 08/12/15 11:39 PM Re: Mysterious Shock [Re: renosteinke]  
twh  Offline
Member
Joined: Mar 2004
Posts: 922
Regina, Sask.
I wonder how much current is available. I'm curious to know how many milliamps are in a tingle.


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